Semiconductor Device and Method for Manufacturing Same

ABSTRACT

A semiconductor device includes a first well and a second well provided within a semiconductor substrate, an isolation region disposed between the first well and the second well within the semiconductor substrate, a first wiring disposed on the first well, a second wiring disposed on the second well, a concave third wiring disposed on the isolation region, a buried insulating film disposed on the third wiring so as to fill the concave portion thereof, a plurality of fourth wirings disposed on the buried insulating film, and a contact plug disposed so as to electrically connect to at least one of the first and second wells.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2013-171305 filed on Aug. 21, 2013, thedisclosure of which are incorporated herein in its entirety byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method formanufacturing the semiconductor device.

2. Description of the Related Art

In recent years, the miniaturization of semiconductor devices has madeprogress, thus resulting in a decrease in the equivalent oxide thickness(EOT) of a gate insulating film. Accordingly, a major increase inleakage current due to the decrease in the EOT has become problematic ina gate insulating film based on a silicon oxynitride film and a siliconoxide film, and a gate electrode structure made from polysilicon whichhave been used. Hence, an HKMG transistor is a focus of attention as anew technique to solve such a problem. The HKMG transistor is atransistor which comprises a gate insulating film including ahigh-dielectric insulating film higher in dielectric constant than oxidesilicon, and a gate electrode including a metal layer. In the HKMGtransistor, the high-dielectric insulating film is used for the gateinsulating film, and therefore, gate leakage currents can be suppressedby increasing the physical thickness of the gate insulating film whiledecreasing the EOT. In addition, use of the gate electrode including themetal layer can improve the operating characteristics of the transistor.

JP2006-24594A and JP2007-329237A disclose the HKMG transistor.

A related method for manufacturing the HKMG transistor will be describedwith reference to FIGS. 26 to 28.

First, as illustrated in FIG. 26A, there is prepared semiconductorsubstrate 1 in which P well 3 and N well 4 are disposed throughisolation region 2. A first laminated film including silicon oxide film5 a, first high-dielectric insulating film 6 a, first metal film 7 a,and impurity-containing polysilicon film 8 a is formed on P well 3, anda second laminated film including silicon oxide film 5 b, firsthigh-dielectric insulating film 6 b, second high-dielectric insulatingfilm 6 c, first metal film 7 b, and impurity-containing polysilicon film8 b is formed on N well 4. At this time, one end 10 a of the firstlaminated film and one end 10 b of the second laminated film arepositioned on isolation region 2. In addition, trench portion 13 isformed of a side surface of end 10 a, a side surface of end 10 b, and afront surface of isolation region 2.

As illustrated in FIG. 26B, impurity-containing polysilicon film 11 andsecond metal film 12 are formed so as to extend in first direction 60indicated above semiconductor substrate 1 from the space on P well 3through the space on isolation region 2 to the space on N well 4. Atthis time, trench portion 13 cannot be completely filled withpolysilicon film 11 and second metal film 12 since the aspect ratio oftrench portion 13 is high, and therefore, seam 14 arises within trenchportion 13. Under this condition, silicon nitride film 15 for use as amask is formed on semiconductor substrate 1 by a plasma CVD method, soas to cover second metal film 12. At this time, silicon nitride film 15fails to completely fill seam 14 since the plasma CVD method is inferiorin coverage (step coverage), and therefore, seam 14 remains withinsilicon nitride film 15.

As illustrated in FIG. 27A, silicon nitride film 15 is patterned to formhard mask 15. The first and second laminated films and portions ofpolysilicon film 11 and second metal film 12 on isolation region 2 arepatterned by etching using hard mask 15. Consequently, first and secondgate electrodes 17 a and 17 b are formed on P well 3 and N well 4,respectively, and wiring 20 is formed on isolation region 2. LDD regions19 a of the N conductivity type are formed within P well 3, and LDDregions 19 b of the P conductivity type are formed within N well 4.Offset spacers 26 a are formed on the side surfaces of first and secondgate electrodes 17 a and 17 b and wiring 20. Thereafter, first sourceand drain 21 a of the N conductivity type are formed within P well 3,and second source and drain 21 b of the P conductivity type are formedwithin N well 4. SOD film 22 is formed on semiconductor substrate 1, andthen CMP treatment or etched back of SOD film 22 is performed to exposehard mask 15. At this time, seam 14 remains as is within wiring 20, andsecond metal film 12 is exposed on the bottom of seam 14.

As illustrated in FIG. 27B, a contact hole to expose therein firstsource and drain 21 a is formed within SOD film 22. Thereafter, anelectrically conductive material is formed so as to fill the contacthole, thereby forming contact plug 24 therein. At this time, seam 14within wiring 20 is also filled with the electrically conductivematerial to form conductive part 20 a.

FIG. 28A is a plan view, and FIG. 28B represents a cross-sectional viewtaken along the A-A′ direction of FIG. 28A. As illustrated in FIGS. 28Aand 28B, wirings 25 a and 25 b are formed on SOD film 22, so as tocontact with hard mask 15. Here, wirings 25 a and 25 b are electricallyconnected to conductive part 20 a since conductive part 20 a has beenformed in the process of FIG. 27B. As a result, the related method hasbeen problematic in that wirings 25 a and 25 b short-circuit to eachother through conductive part 20 a.

SUMMARY

In one embodiment, there is provided a semiconductor device comprising:

-   -   a first well and a second well provided within a semiconductor        substrate;    -   an isolation region disposed between the first well and the        second well within the semiconductor substrate;    -   a first wiring disposed on the first well;    -   a second wiring disposed on the second well;    -   a concave third wiring disposed on the isolation region;    -   a buried insulating film disposed on the third wiring so as to        fill a concave portion thereof;    -   a plurality of fourth wirings disposed on the buried insulating        film; and    -   a contact plug disposed so as to electrically connect to at        least one of the first and second wells.

In another embodiment, there is provided a method for manufacturing asemiconductor device, comprising:

-   -   preparing a semiconductor substrate including a first well, a        second well, and an isolation region between the first well and        the second well with respect to a first direction;    -   forming a first conductive film which is located on the first        well and one end of which in the first direction is positioned        on the isolation region, and a second conductive film which is        located on the second well and one end of which in the first        direction is positioned on the isolation region;    -   forming a third conductive film, so as to extend from a space on        the first conductive film through a space on the isolation        region to a space on the second conductive film with respect to        the first direction, and have a concave shape on the isolation        region;    -   forming a buried insulating film on the third conductive film,        so as to fill a concave portion of the third conductive film on        the isolation region;    -   patterning the first to third conductive films and the buried        insulating film to form a first wiring on the first well, a        second wiring on the second well, and a concave third wiring and        a buried insulating film on the isolation region;    -   forming an interlayer insulating film on the semiconductor        substrate;    -   removing a portion of the interlayer insulating film until the        buried insulating film is exposed;    -   forming a contact plug, so as to penetrate through the        interlayer insulating film, resulting in contacting with at        least one of the first and second wells; and    -   forming a plurality of fourth wirings, so as to contact with the        buried insulating film on the third wiring.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be moreapparent from the following description of certain preferred embodimentstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view illustrating a semiconductor device according tothe first exemplary embodiment.

FIG. 2 is a cross-sectional view illustrating a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 3 is a cross-sectional view illustrating a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 4 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 5 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 6 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 7 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 8 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 9 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 10 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 11 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 12 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 13 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 14 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 15 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 16 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 17 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 18 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 19 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 20 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 21 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 22 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 23 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 24 illustrates a method of manufacturing a semiconductor deviceaccording to the first exemplary embodiment.

FIG. 25 illustrates a method of manufacturing a semiconductor deviceaccording to the second exemplary embodiment.

FIG. 26 illustrates a related method of manufacturing a semiconductordevice.

FIG. 27 illustrates a related method of manufacturing a semiconductordevice.

FIG. 28 illustrates a related method of manufacturing a semiconductordevice.

In the drawings, numerals have the following meanings, 1: semiconductorsubstrate, 1 a: active region, 2: isolation region, 2 a, 52: siliconnitride film, 2 b, 51, 58 a, 58 b: silicon oxide film, 3: P well, 4: Nwell, 5 a, 5 b: silicon oxide film, 6 a, 6 b: hafnium oxide film (firsthigh-dielectric insulating film), 6 c: aluminum oxide film (secondhigh-dielectric insulating film), 7 a, 7 b: first metal film, 8 a, 8 b,11, 11 a, 11 b, 11 c, 11 d: impurity-containing polysilicon film, 10 a,10 b, 10 c, 10 d: end, 12, 12 a, 12 b, 12 c, 12 d: second metal film,13: trench portion, 14: seam (concave portion), 15: silicon nitridefilm, 15 a: buried insulating film, 15 b: second insulating film, 15 c:first insulating film, 17 a: first gate electrode, 17 b: second gateelectrode, 19 a, 19 b: LDD region, 20, 25 a, 25 b: wiring, 20 a:conductive part, 20′: third wiring, 21 a: first source and drain, 21 b:second source and drain, 22: SOD film, 24: contact plug, 25 c, 25 d:fourth wiring, 25 e: fifth wiring, 26 a: offset spacer, 26 b: sidewallspacer, 30: word line (buried gate electrode), 30′: dummy word line, 30a: barrier metal film, 30 b: metal gate film, 31: bit line, 32 a:capacitor contact region, 32 b, 32 d: capacitor contact plug, 32 c:capacitor contact pad, 33: bit contact region, 37: third gate insulatingfilm, 38 a: liner film, 38 b: SOD film, 39: bit contact interlayerinsulating film, 43: liner film, 45: stopper film, 48: capacitor, 48 a:lower electrode, 48 b: capacitor insulating film, 48 c: upper electrode,55: trench, 60: first direction, Cn: region for forming NMOS, Cp: regionfor forming PMOS, Tr1: first transistor, Tr2: second transistor, andTr3: third transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be now described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teachings ofthe present invention and that the invention is not limited to theembodiments illustrated for explanatory purposes.

In one example of a semiconductor device and the manufacturing methodthereof according to the present invention, a concave third wiring isdisposed on an isolation region. In addition, a buried insulating filmsuperior in coverage (step coverage) is formed so as to fill the concaveportion of the third wiring. Consequently, even if a plurality of fourthwirings are formed on the buried insulating film, the third wiring andthe fourth wirings are isolated from each other by the buried insulatingfilm. Thus, it is possible to prevent a plurality of adjacent fourthwirings from short-circuiting to one another through the third wiring todegrade device characteristics.

Hereinafter, the semiconductor device and the manufacturing methodthereof which are embodiments to which the present invention is appliedwill be described with reference to the accompanying drawings. Note thatthe drawings used in the following description are merely schematic, andlength, width and thickness ratios and the like among respectivedrawings are not necessarily the same as actual ratios. Accordingly,length, width and thickness ratios and the like among respectivedrawings may not coincide with one another. In addition, conditions,such as materials and dimensions, specifically shown in the followingembodiments are examples only.

Note that in the following embodiments, “first transistor” refers to anN-channel MOS transistor (hereinafter described as “NMOS” in some cases)formed in a peripheral circuit region, “Second transistor” refers to aP-channel MOS transistor (hereinafter described as “PMOS” in some cases)formed in the peripheral circuit region. “Third transistor” refers to atransistor formed in a memory cell region.

“First wiring” and “second wiring” respectively refer to first gateelectrode 17 a formed on P well 3 and second gate electrode 17 b formedon N well 4 in the peripheral circuit region. “First well” and “secondwell” respectively refer to a P well and an N well. “First conductivefilm” refers to first metal film 7 a and impurity-containing polysiliconfilm 8 a formed on P well 3 of the peripheral circuit region (see, forexample, FIG. 15). “Second conductive film” refers to first metal film 7b and impurity-containing polysilicon film 8 b formed on N well 4 of theperipheral circuit region (see, for example, FIG. 15). “Third conductivefilm” refers to impurity-containing polysilicon film 11 and second metalfilm 12 (see, for example, FIG. 16).

First Exemplary Embodiment 1. Semiconductor Device

The present exemplary embodiment relates to a DRAM (Dynamic RandomAccess Memory) which is a semiconductor device to which a structure ofthe present invention is applied.

FIGS. 1 to 3 are schematic views illustrating the semiconductor deviceof the present exemplary embodiment, where FIG. 1A is a plan view of amemory cell region, FIG. 1B is a plan view of a peripheral circuitregion, FIG. 2 is a cross-sectional view taken along the A-A′ directionof FIG. 1A, and FIG. 3 is a cross-sectional view taken along the A-A′direction of FIG. 1B. Note that the plan views of FIG. 1 represent onlymajor structures of the semiconductor device.

The DRAM of the present exemplary embodiment is composed of the memorycell region illustrated in FIG. 1A and the peripheral circuit regionillustrated in FIG. 1B, and has a 6F2 cell layout (F denotes a minimumis processing size).

(Memory Cell Region)

As illustrated in FIG. 1A, a plurality of isolation regions (STI) 2 anda plurality of active regions 1 a are alternately formed atpredetermined intervals in a Y direction in the memory cell region ofthe DRAM. Isolation regions 2 and active regions 1 a extend in an X′direction shown in FIG. 1A. In addition, buried gate electrodes 30 toserve as word lines and dummy word lines 30′ extend in a Y direction, soas to come across active regions 1 a. Buried gate electrodes 30 anddummy word lines 30′ are formed as the result of being buried insemiconductor substrate 1 at predetermined intervals in an X direction.Yet additionally, a plurality of bit lines 31 is disposed atpredetermined intervals in the X direction orthogonal to word lines 30and dummy word lines 30′. A memory cell is formed in a region in whichword line 30 and active region 1 a intersect with each other. Eachmemory cell is composed of third transistor Tr3 and an unillustratedcapacitor. Third transistor Tr3 is composed of capacitor contact region32 a and bit contact region 33 to serve as a third source and drain,word line 30, and an unillustrated third gate insulating film.

Word lines 30 and dummy word lines 30′ are the same in structure butdifferent in functionality. Whereas each word line 30 is used as thegate electrode of third transistor Tr3, dummy word line 30′ is providedin order to isolate adjacent third transistors Tr3 from each other byapplying a predetermined potential. That is, third transistors adjacentto each other on the same active region 1 a are isolated from each otherby maintaining dummy word line 30′ at a predetermined potential andthereby turning off parasitic transistors. In addition, a plurality ofmemory cells are formed in the memory cell region as a whole, and acapacitor (not illustrated in FIG. 1A) is provided in each memory cell.Each capacitor is electrically connected to capacitor contact region 32a through capacitor contact plugs 32 b and 32 d electrically connectedto capacitor contact region 32 a of each transistor and throughcapacitor contact pad 32 c electrically connected to capacitor contactplugs 32 b and 32 d. As illustrated in FIG. 1A, capacitor contact plugs32 b and 32 d are disposed at predetermined intervals within the memorycell region, so as not to overlap with each other. In addition, eachmemory cell is connected to bit line 31 through bit contact region 33.

As illustrated in FIG. 2, each memory cell is formed of third transistorTr3 and capacitor 48 in the memory cell region. Third transistor Tr3 iscomposed of word line 30 formed of a buried gate electrode buried insemiconductor substrate 1, third gate insulating film 37 disposedbetween semiconductor substrate 1 and word line 30, and capacitorcontact region 32 a and bit contact region 33 disposed on the principalsurface of semiconductor substrate 1 to serve as a third source anddrain. Each word line 30 is composed of, for example, barrier metal film30 a made of a titanium nitride film and metal gate film 30 b made of atungsten film. Each word line 30 is formed so that the upper surfacethereof is lower than the upper surface of semiconductor substrate 1.Liner film 38 a made of a silicon nitride film and SOD (Spin onDielectric) film 38 b are disposed on each word line 30.

Bit contact interlayer insulating film 39 made of a silicon nitride filmis disposed on semiconductor substrate 1. A portion of bit contactinterlayer insulating film 39 on bit contact region 33 is open, and bitline 31 is disposed in the portion, so as to contact with bit contactregion 33. Bit line 31 is composed of, for example, impurity-containingpolysilicon film 11 d and laminated film 11 e made of a tungsten nitridefilm and a tungsten film, in order from the side nearest tosemiconductor substrate 1. Buried insulating film 15 a made of a siliconnitride film is disposed on bit line 31. Liner film 43 made of a siliconnitride film is disposed on bit contact interlayer insulating film 39and on the side surfaces of bit line 31 and buried insulating film 15 a.SOD film (interlayer insulating film) 22 is disposed on liner film 43.

Capacitor contact plugs 32 b and 32 d are disposed so as to penetratethrough SOD film 22, liner film 43 and bit contact interlayer insulatingfilm 39 and connect to capacitor contact region 32 a. Capacitor contactpad 32 c is further disposed on SOD film 22, so as to connect tocapacitor contact plugs 32 b and 32 d. Stopper film 45 made of a siliconnitride film and an interlayer insulating film (not illustrated) aredisposed on SOD film 22, so as to cover capacitor contact pad 32 c. Inaddition, capacitor 48 is disposed so as to electrically connect tocapacitor contact pad 32 c. Capacitor 48 is electrically connected tocapacitor contact region 32 a through capacitor contact plugs 32 b and32 d and capacitor contact pad 32 c. Note that capacitor contact pad 32c may not be formed. In that case, capacitor 48 is formed on capacitorcontact plug 32 d as appropriate. Capacitor 48 is formed as the resultof lower electrode 48 a, capacitor insulating film 48 b and upperelectrode 48 c being laminated in this order.

(Peripheral Circuit Region)

As illustrated in FIG. 1B, region Cn for forming an NMOS is formed andregion Cp for forming a PMOS is formed are disposed in the peripheralcircuit region. Regions Cn and Cp are disposed so as to sandwich anunillustrated isolation region (STI) therebetween. Active regions 1 a inwhich surfaces of semiconductor substrate 1 are exposed are disposed inregions Cn and Cp, and first gate electrode (first wiring) 17 a andsecond gate electrode (second wiring) 17 b formed simultaneously withthe formation of bit lines 31 of the memory cell region are disposed soas to halve respective active regions 1 a. In region Cn, ahigh-concentration impurity is introduced into active regions 1 a onboth sides of first gate electrode 17 a to convert the active regionsinto first source and drain 21 a. Likewise, in region Cp, ahigh-concentration impurity is introduced into active regions 1 a onboth sides of second gate electrode 17 b to convert the active regionsinto second source and drain 21 b. First gate electrode 17 a, firstsource and drain 21 a, and an unillustrated first gate insulating filmformed on region Cn constitute first transistor Tr1 in the peripheralcircuit region. Likewise, second gate electrode 17 b, second source anddrain 21 b, and an unillustrated second gate insulating film formed onregion Cp constitute second transistor Tr2 in the peripheral circuitregion. First source and drain 21 a is connected to fifth wiring 25 ethrough contact plug 24.

Third wiring 20′ is formed on the isolation region. A seam is present inthe upper portion of third wiring 20′, thus causing the wiring to beconcave-shaped. An unillustrated buried insulating film is disposed onthird wiring 20′, so as to fill the seam (concave portion). Fourthwirings 25 c and 25 d are disposed on the buried insulating film. Thirdwiring 20′ and fourth wirings 25 c and 25 d are isolated from each otherthrough the buried insulating film disposed on third wiring 20′.Consequently, it is possible to prevent fourth wirings 25 c and 25 dfrom short-circuiting to each other through third wiring 20′ to degradedevice characteristics.

As illustrated in FIG. 3, the peripheral circuit region of thesemiconductor device of the present exemplary embodiment includes P well3 and N well 4. Isolation region 2 is disposed between P well 3 and Nwell 4 to insulate and separate P well 3 and N well 4 from each other.Isolation region 2 is composed of a laminated film made of silicon oxidefilm 2 b and silicon nitride film 2 a. Silicon oxide film 5 a andhafnium oxide film (first high-dielectric insulating film) 6 a servingas first gate insulating films are disposed on P well 3 in this order.Titanium nitride film (first metal film) 7 a, impurity-containingpolysilicon films 8 a and 11 a, and first gate electrode (first wiring)17 a composed of laminated film (second metal film) 12 a made of atungsten nitride film and a tungsten film are disposed on the first gateinsulating films. Silicon oxide film 5 b, hafnium oxide film (firsthigh-dielectric insulating film) 6 b, and aluminum oxide film (secondhigh-dielectric insulating film) 6 c serving as second gate insulatingfilms are disposed on N well 4 in this order. Titanium nitride film(first metal film) 7 b, impurity-containing polysilicon films 8 b and 11b, and second gate electrode 17 b composed of laminated film (secondmetal film) 12 b made of a tungsten nitride film and a tungsten film aredisposed on the second gate insulating films. Buried insulating films 15a are disposed on first and second gate electrodes 17 a and 17 b.

Concave third wiring 20′ is formed on isolation region 2. Third wiring20′ is composed of impurity-containing polysilicon film 11 c andlaminated film (second metal film) 12 c made of a tungsten nitride filmand a tungsten film, where the upper portion of third wiring 20′ isconcave-shaped. Buried insulating film 15 a superior in coverage (stepcoverage) is disposed so as to fill the concave portion of third wiring20′. Offset spacer 26 a made of a silicon nitride film, sidewall spacer26 b made of a silicon oxide film, and liner film 26 c made of a siliconnitride film are disposed in order on the side surfaces of first gateelectrodes 17 a, second gate electrodes 17 b, and third wiring 20′,respectively.

LDD regions 19 a of the N conductivity type and first source and drain21 a of the N conductivity type are respectively formed on both sides offirst gate electrode 17 a within P well 3. LDD regions 19 b of the Pconductivity type and second source and drain 21 b of the P conductivitytype are respectively formed on both sides of second gate electrode 17 bwithin N well 4. P well 3, first gate insulating films 5 a and 6 a,first gate electrode 17 a, LDD regions 19 a of the N conductivity type,and first source and drain 21 a constitute the NMOS which is firsttransistor Tr1. In addition, N well 4, second gate insulating films 5 b,6 b and 6 c, second gate electrode 17 b, LDD regions 19 b of the Pconductivity type, and second source and drain 21 b constitute the PMOSwhich is second transistor Tr2.

SOD film (interlayer insulating film) 22 is disposed on semiconductorsubstrate 1 within the peripheral circuit region. Contact plug 24 isdisposed so as to penetrate through SOD film 22 and connect to firstsource and drain 21 a. Fifth wiring 25 e is disposed on SOD film 22, soas to contact with contact plug 24, and fourth wiring 25 c is disposedso as to contact with buried insulating film 15 a on third wiring 20′.

2. Method for Manufacturing Semiconductor Device

Hereinafter, a method for manufacturing a semiconductor device of thepresent exemplary embodiment will be described with reference to FIGS. 1to 23. Note that in FIGS. 4 to 11, 16 to 19 and 22 to 24, each view Arepresents a cross-sectional view corresponding to the A-A′ direction ofthe memory cell region in FIG. 1A, whereas each view B represents across-sectional view corresponding to the A-A direction of theperipheral circuit region in FIG. 1B. FIGS. 12 to 15 and 20 to 21represent cross-sectional views corresponding to the A-A′ direction ofthe peripheral circuit region in FIG. 1B.

First, as illustrated in FIG. 4, isolation region (STI) 2 composed of alaminated film made of silicon oxide film 2 b and silicon nitride film 2a is formed in the memory cell region and the peripheral circuit regionwithin semiconductor substrate 1 (the isolation region is notillustrated in FIG. 4A). Consequently, active region 1 a divided off byisolation region 2 is defined in the memory cell region and theperipheral circuit region. In addition, P well 3 and N well 4 are formedwithin active region 1 a by a heretofore-known method. An impurity isimplanted into semiconductor substrate 1 in the memory cell region toform an impurity-diffused layer. Subsequently, the principal surface ofsemiconductor substrate 1 is thermally oxidized to form silicon oxidefilm 51, and silicon nitride film 52 is formed on silicon oxide film 51.Silicon oxide film 51 and silicon nitride film 52 on the memory cellregion are patterned to provide a hard mask pattern. Groove-like trench55 extending in a direction intersecting with the isolation region isformed in semiconductor substrate 1 by etching using the hard maskpattern. This formation of trench 55 splits the previously-formedimpurity-diffused layer into capacitor contact region 32 a and bitcontact region 33 which are a third source and drain.

As illustrated in FIG. 5, the inner walls of trench 55 are oxidized byan ISSG (in-situ steam generation) method to form third gate insulatingfilm 37 made of a silicon oxide film. Next, barrier film 30 a, such as atitanium nitride film, is formed on the inner walls of trench 55.

As illustrated in FIG. 6, trench 55 is filled with metal gate film 30 b,such as a tungsten film.

As illustrated in FIG. 7, the upper surfaces of barrier film 30 a andmetal gate film 30 b are backed away from the principal surface ofsemiconductor substrate 1 by etch-back to form word line (buried gateelectrode) 30. Consequently, there are formed capacitor contact region32 a and bit contact region 33 to serve as a third source and drain,third gate insulating film 37, and third transistor Tr3 including wordline (buried gate electrode) 30.

As illustrated in FIG. 8, liner film 38 a made of a silicon nitride filmis formed on the entire surface of semiconductor substrate 1, and thenSOD film 38 b is further formed thereon. Thereafter, a CMP treatment isperformed on SOD film 38 b until the upper surface of liner film 38 a isexposed.

As illustrated in FIG. 9, upper portions of liner film 38 a and SOD film38 b are removed by dry etching. Next, silicon nitride film 52 isremoved by dry etching.

As illustrated in FIG. 10, bit contact interlayer insulating film 39made of a silicon nitride film is formed on the entire surface ofsemiconductor substrate 1.

As illustrated in FIG. 11, bit contact interlayer insulating film 39 andsilicon oxide film 51 deposited in the peripheral circuit region areremoved in order using photolithographic and etching methods to exposethe principal surface of semiconductor substrate 1.

Next, as illustrated in FIG. 12, the surfaces of P well 3 and N well 4in the peripheral circuit region are thermally oxidized to form siliconoxide films 5 a and 5 b, respectively. Hafnium oxide film (firsthigh-dielectric insulating film) 6 is formed on the entire surface ofsemiconductor substrate 1 by an ALD or CVD method. Thereafter, titaniumnitride film (first metal film) 7 a, impurity-containing polysiliconfilm 8 a, and silicon oxide film 58 a are formed on the entire surfaceof semiconductor substrate 1.

As illustrated in FIG. 13, silicon oxide film 58 a is patterned usinglithography and dry etching techniques to form a hard mask made ofsilicon oxide film 58 a, so as to cover P well 3. Polysilicon film 8 aand first metal film 7 a are dry-etched using hard mask 58 a.Consequently, a first conductive film made of first metal film 7 a andpolysilicon film 8 a is disposed on P well 3. At this time, hard mask 58a, polysilicon film 8 a, and first metal film 7 a deposited in thememory cell region are also removed at the same time.

As illustrated in FIG. 14, aluminum oxide film (second high-dielectricinsulating film) 6 c is formed on the entire surface of semiconductorsubstrate 1 by an ALD or PVD method. Thereafter, titanium nitride film(first metal film) 7 b, impurity-containing polysilicon film 8 b, andsilicon oxide film 58 b are formed on the entire surface ofsemiconductor substrate 1.

As illustrated in FIG. 15, silicon oxide film 58 b (not illustrated) ispatterned using lithography and dry etching techniques to form a hardmask made of silicon oxide film 58 b, so as to cover N well 4.Polysilicon film 8 b, first metal film 7 b, hafnium oxide film 6 b, andaluminum oxide film 6 c are dry-etched using hard mask 58 b.Consequently, silicon oxide film 5 b, hafnium oxide film 6 b, aluminumoxide film 6 c, and a second conductive film made of first metal film 7b and polysilicon film 8 b are disposed on N well 4. In addition,silicon oxide film 5 a, hafnium oxide film 6 a, and the first conductivefilm made of first metal film 7 a and polysilicon film 8 a are disposedon P well 3. At this time, silicon oxide film 58 b, polysilicon film 8b, first metal film 7 b, hafnium oxide film 6 b, and aluminum oxide film6 c deposited in the memory cell region are also removed at the sametime to expose bit contact interlayer insulating film 39. At this point,one end 10 c each of hafnium oxide film 6 a and the first conductivefilm in first direction 60 is positioned on isolation region 2.Likewise, one end 10 d each of hafnium oxide film 6 b, aluminum oxidefilm 6 c, and the second conductive film in first direction 60 ispositioned on isolation region 2. In addition, trench portion 13 iscomposed of ends 10 c and 10 d and isolation region 4.

As illustrated in FIG. 16, portions of bit contact interlayer insulatingfilm 39 and silicon oxide film 51 on bit contact region 33 located inthe memory cell region are removed using photolithographic and etchingmethods to expose bit contact region 33. In addition, hard masks 58 aand 58 b in the peripheral circuit region are removed by wet etching.

As illustrated in FIG. 17, impurity-containing polysilicon film 11 andlaminated film (second metal film) 12 made of a tungsten nitride filmand a tungsten film are formed on the entire surface of semiconductorsubstrate 1. At this time, polysilicon film 11 and second metal film 12are formed in the peripheral circuit region, so as to extend from aspace on the first conductive film through a space on isolation region 2to a space on the second conductive film in first direction 60, asillustrated in FIG. 17B. Seam (concave portion) 14 arises aboveisolation region 2 of the peripheral circuit region since polysiliconfilm 11 and second metal film 12 are formed within trench portion 13having high aspect ratio.

As illustrated in FIG. 18, silicon nitride film (buried insulating film)15 a is formed on the entire surface of semiconductor substrate 1 by anALD (Atomic Layer Deposition) method. Since silicon nitride film 15 asuperior in coverage (step coverage) can be formed in the ALD method, itis possible to fill seam (concave portion) 14 with silicon nitride film15 a. Next, silicon nitride film (second insulating film) 15 b is formedon silicon nitride film 15 a by a plasma CVD method. Whereas the ALDmethod is low in the rate of film formation, the plasma CVD method canachieve a high rate of film formation. Accordingly, it is possible toreduce the film-forming time of the silicon nitride films as a whole andimprove throughputs, while filling seam 14 with silicon nitride film 15a, by forming silicon nitride film 15 b by the plasma CVD method aftersilicon nitride film 15 a is formed by the ALD method.

As illustrated in FIG. 19B, silicon nitride films 15 a and 15 b arepatterned using lithography and dry etching techniques to form hardmasks made of silicon nitride films 15 a and 15 b on P well 3, N well 4and isolation region 2 in the peripheral circuit region. Second metalfilm 12, polysilicon films 8 a, 8 b and 11, first metal films 7 a and 7b, hafnium oxide films 6 a and 6 b, aluminum oxide film 6 c, and siliconoxide films 5 a and 5 b in the peripheral circuit region are dry-etchedusing the hard masks. Consequently, silicon oxide film 5 a and hafniumoxide film 6 a are formed on P well 3 as first gate insulating films,and first gate electrode (first wiring) 17 a including first metal film7 a, polysilicon films 8 a and 11 a, and second metal film 12 a is alsoformed on the P well. Likewise, silicon oxide film 5 b, hafnium oxidefilm 6 b and aluminum oxide film 6 c are formed on N well 4 as secondgate insulating films, and second gate electrode (second wiring) 17 bincluding first metal film 7 b, polysilicon films 8 b and 11 b, andsecond metal film 12 b is also formed on the N well. In addition, thirdwiring 20′ including polysilicon film 11 c and second metal film 12 c isformed on isolation region 2.

As illustrated in FIG. 19A, silicon nitride films 15 a and 15 b arepatterned in the memory cell region simultaneously with the process ofFIG. 19B to form a hard mask on bit contact region 33. Second metal film12 and polysilicon film 11 in the memory cell region are dry-etchedusing the hard mask. Consequently, bit line 31 including polysiliconfilm 11 d and second metal film 12 d is formed on bit contact region 33.

As described above, hard masks made of silicon nitride films 15 a and 15b are disposed on first and second gate electrodes 17 a and 17 b, thirdwiring 20′ and bit line 31.

As illustrated in FIG. 20, a silicon nitride film is formed on theentire surface of semiconductor substrate 1 and then etched back,thereby forming offset spacers 26 a on the side surfaces of first andsecond gate electrodes 17 a and 17 b and third wiring 20′. LDD regions19 a are formed by implanting an impurity of the N conductivity typeinto P well 3 using hard masks 15 a and 15 b and offset spacer 26 a asmasks. LDD regions 19 b are formed by implanting an impurity of the Pconductivity type into N well 4 using hard masks 15 a and 15 b andoffset spacer 26 a as masks.

As illustrated in FIG. 21, a silicon oxide film is formed on the entiresurface of semiconductor substrate 1, and then a portion of the siliconoxide film deposited in the memory cell region is selectively removedusing lithography and wet etching techniques. Thereafter, a portion ofthe silicon oxide film in the peripheral circuit region is etched backto form sidewall spacers 26 b on the side surfaces of first and secondgate electrodes 17 a and 17 b and third wiring 20′. An impurity of the Nconductivity type is implanted into P well 3 using hard masks 15 a and15 b, offset spacers 26 a and sidewall spacers 26 b as masks to formfirst source and drain 21 a. An impurity of the P conductivity type isimplanted into N well 4 using hard masks 15 a and 15 b, offset spacers26 a and sidewall spacers 26 b as masks to form second source and drain21 b.

As illustrated in FIG. 22, liner film 26 c made of a silicon nitridefilm is formed on the entire surface of semiconductor substrate 1, so asto cover first and second gate electrodes 17 a and 17 b and third wiring20′ in the peripheral circuit region and bit line 31 in the memory cellregion. A coating-based insulating film is formed on the entire surfaceof semiconductor substrate 1 and then anneal-treated to form SOD film22.

Next, as illustrated in FIG. 23, a contact hole is formed so as topenetrate through SOD film 22, liner film 43, bit contact interlayerinsulating film 39 and silicon oxide film 51 and expose capacitorcontact region 32 a. After the contact hole is filled with a polysiliconfilm, the polysilicon film, silicon nitride film (not illustrated) 15 band SOD film 22 are CMP-treated and planarized. At this time, siliconnitride film 15 b formed by a plasma CVD method is removed so that onlysilicon nitride film 15 a formed by an ALD method remains on first andsecond gate electrodes 17 a and 17 b, third wiring 20′ and bit line 31.In addition, the polysilicon film is etched back to recess the uppersurface thereof, thereby forming capacitor contact plugs 32 b.

Next, as illustrated in FIG. 24, a contact hole is formed within SODfilm 22 using lithography and dry etching techniques, so as to exposefirst source and drain 21 a. An electrically conductive material, suchas tungsten, is filled in the contact hole to form contact plug 24. Atthis time, the electrically conductive material, such as tungsten, isalso deposited on capacitor contact plug 32 b in the memory cell region,thus forming capacitor contact plug 32 d. Next, the conductive film madefrom tungsten or the like is patterned using lithography and dry etchingtechniques. Consequently, a plurality of fourth wirings are formed (seeFIG. 1B only one fourth wiring 25 c is shown in FIG. 24B), so as tocontact with silicon nitride film 15 a on SOD film 22 (third wiring20′), and fifth wiring 25 e is formed so as to contact with contact plug24. At this point, capacitor contact pad 32 c is formed at the sametime, so as to contact with capacitor contact plug 32 d.

Subsequently, as illustrated in FIGS. 1A and 2, stopper film 45 made ofa silicon nitride film and an interlayer insulating film (notillustrated) are formed so as to cover capacitor contact pad 32 c. Acylinder hole is formed so as to expose capacitor contact pad 32 cwithin the interlayer insulating film and stopper film 45, and thenlower electrode 48 a is formed on the inner wall surfaces of thecylinder hole. Thereafter, the interlayer insulating film in the memorycell region is removed to expose the outer lateral surfaces of lowerelectrode 48 a. Capacitor insulating film 48 b is formed on the exposedsurfaces of lower electrode 48 a, and then upper electrode 48 c isfurther formed so as to cover lower electrode 48 a and capacitorinsulating film 48 b. Consequently, there is completed crown-shapedcapacitor 48 composed of lower electrode 48 a, capacitor insulating film48 b and upper electrode 48 c.

In the present exemplary embodiment, seam (concave portion) 14 of thirdwiring 20′ is filled with silicon nitride film (buried insulating film)15 a. Accordingly, there is no such possibility that an electricallyconductive material is filled in seam 14 in the process of forming aconductive film after the formation of the third wiring (the process offorming contact plug 24 and capacitor contact plug 32 d in the presentexemplary embodiment). Consequently, third wiring 20′ can be preventedfrom electrically connecting to the plurality of fourth wirings. As aresult, it is possible to prevent the plurality of fourth wirings fromshort-circuiting to one another through third wiring 20′ to degradedevice characteristics.

Second Exemplary Embodiment

The present exemplary embodiment differs in that instead of theprocesses of FIGS. 17 and 18 in the first exemplary embodiment, siliconnitride film 15 c is formed by a plasma CVD method after polysiliconfilm 11 and second metal film 12 are formed and, thereafter, siliconnitride film 15 a is formed by an ALD method and silicon nitride film 15b is formed by a plasma CVD method. The present exemplary embodiment isthe same as the first exemplary embodiment except that the process ofFIG. 25 is carried out instead of the processes of FIGS. 17 and 18 inthe first exemplary embodiment, and therefore, only the process of FIG.25 will be described here.

In the process of FIG. 25, silicon nitride film (first insulating film)15 c is formed first by a plasma CVD method. Since this plasma CVDmethod is not superior in coverage (step coverage), it is not possibleto completely fill seam 14 (concave portion) above isolation region 2 inthe peripheral circuit region with silicon nitride film 15 c. It ispossible to fill seam 14 (concave portion) above isolation region 2 withsilicon nitride film 15 a, however, by subsequently forming siliconnitride film (buried insulating film) 15 a using an ALD method.Thereafter, silicon nitride film (first insulating film) 15 b is furtherformed by a plasma CVD method.

In the present exemplary embodiment, silicon nitride film 15 c is formedfirst by a plasma CVD method and, thereafter, silicon nitride film 15 afor filling seam 14 is formed by an ALD method. The plasma CVD method ishigher in the rate of film formation than the ALD method. Accordingly,it is possible to further improve throughputs, compared with the firstexemplary embodiment in which silicon nitride film 15 a is formed usingthe ALD method from the beginning until seam 14 is filled. Note that aplurality of films may be formed in seam 14 of third wiring 20′ by goingthrough a plurality of film formation processes. In this case, at leastone film formation process superior in coverage needs to be applied inorder to completely fill seam 14 with a film. In other film formationprocesses, however, films inferior in coverage may be formed or filmssuperior in coverage may be formed.

In the first and second exemplary embodiments, silicon nitride film 15 ais formed by an ALD method, in order to fill seam 14 above isolationregion 4 in the peripheral circuit region. However, a film-formingmethod for filling seam 14 is not limited to an ALD method. Otherfilm-forming methods may be used as long as the methods are superior incoverage and capable of filling seam 14. As such film-forming methods,it is possible to use, for example, a low-pressure CVD (LPCVD:Low-Pressure Chemical Vapor Deposition) method or a plasma CVD methodlower in the rate of film formation than a plasma CVD method used in thefirst and second exemplary embodiments.

Third Exemplary Embodiment

The present exemplary embodiment differs from the first and secondexemplary embodiments in that a silicon nitride film is formed by aplasma CVD method superior in coverage to fill the seam of the thirdwiring. More specifically, silicon nitride film 15 a is formed by aplasma CVD method superior in coverage in the process of FIG. 18 in thefirst exemplary embodiment. Alternatively, at least one of siliconnitride films 15 a and 15 b is formed by a plasma CVD method superior incoverage in the process of FIG. 25 in the second exemplary embodiment.Specific film-forming conditions for the CVD method to be superior incoverage are not limited in particular. It is possible to adjustfilm-forming conditions as appropriate, according to the properties ofthe seam of the third wiring. For example, a raw material gas issufficiently supplied into the seam by increasing a source gas (SiH₄,NH₃ or the like) and decreasing a carrier gas (N₂ or the like) at thetime of film formation, thereby performing film formation so that afilm-forming reaction adequately takes place within the seam. Inaddition, RF high-frequency power is decreased at the time of filmformation to lower the rate of film formation, thereby allowing a rawmaterial gas to adequately reach the interiors of the seam. RFlow-frequency power is slightly increased to improve the directionalityof a source gas toward a substrate in which the third wiring is formed.

Also in the present exemplary embodiment, it is possible to form aburied insulating film superior in coverage (step coverage), so as tofill the concave portion of the third wiring. Consequently, it ispossible to prevent a plurality of adjacent fourth wirings fromshort-circuiting to one another through the third wiring to degradedevice characteristics.

In the first to third exemplary embodiments, first metal films 6 a and 6b may be made of the same material or different materials. For example,in a case where different materials are used to set work functionsseparately for first metal films 6 a and 6 b, the NMOS may be composedof gate electrode which includes material other than a titanium nitridefilm, for example, a TaN, and the PMOS may be composed of a gateelectrode containing a titanium nitride film. In addition, the gateelectrodes of both MOS transistors may contain TiN and polysilicon, thegate electrode of the PMOS may contain Al, and the gate electrode of theNMOS may contain La or Mg. In a case where the same material is used forfirst metal films 6 a and 6 b, the same material, such as TiSiN, TaN orTiN, may be used for the gate electrodes of the NMOS and the PMOS to setwork functions separately by varying the thicknesses of the electrodes.

The materials of the high-dielectric insulating films used in the firstto third exemplary embodiments are not limited in particular, as long asthe materials are higher in dielectric constant than oxide silicon. Itis possible to use at least one insulating material selected from thegroup consisting of HfSiO, HfSiON, ZrO₂, ZrSiO, ZrSiON, Ta₂O₅, Nb₂O₅,Al₂O₃, HfO₂, ScO₃, Y₂O₃, La₂O₃, CeO₃, Pr₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃,Tb₂O₃, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃ and Lu₂O_(3.)

The second metal films used in the first to third exemplary embodimentsare not limited in particular. In addition to the second metal filmsshown in the first to third exemplary embodiments, it is possible touse, for example, a laminated film composed of a tungsten silicide film,a tungsten nitride film and a tungsten film.

It is apparent that the present invention is not limited to the aboveembodiments, but may be modified and changed without departing from thescope and spirit of the invention.

What is claimed is:
 1. A semiconductor device comprising: a first well and a second well provided within a semiconductor substrate; an isolation region disposed between the first well and the second well within the semiconductor substrate; a first wiring disposed on the first well; a second wiring disposed on the second well; a concave third wiring disposed on the isolation region; a buried insulating film disposed on the third wiring so as to fill a concave portion thereof; a plurality of fourth wirings disposed on the buried insulating film; and a contact plug disposed so as to electrically connect to at least one of the first and second wells.
 2. The semiconductor device according to claim 1, further comprising: a first transistor including the first wiring, a first gate insulating film between the first wiring and the first well, a first source and drain disposed on both sides of the first wiring within the first well; and a second transistor including the second wiring, a second gate insulating film between the second wiring and the second well, a second source and drain disposed on both sides of the second wiring within the second well, wherein the first wiring is a first gate electrode of the first transistor, the second wiring is a second gate electrode of the second transistor, and the contact plug is electrically connected to at least one of the first source and drain and the second source and drain.
 3. The semiconductor device according to claim 2, comprising: a memory cell region provided with a memory cell including a third transistor comprising a third source and drain and a capacitor electrically connected to one of the third source and drain; and a peripheral circuit region including the first and second transistors, the third and fourth wirings, the buried insulating film, and the contact plug.
 4. The semiconductor device according to claim 1, wherein the buried insulating film is formed by an ALD method or a low-pressure CVD method.
 5. The semiconductor device according to claim 1, further comprising a first insulating film between the third wiring and the buried insulating film.
 6. The semiconductor device according to claim 1, further comprising a second insulating film on the buried insulating film.
 7. The semiconductor device according to claim 2, wherein the first wiring includes a first metal film, an impurity-containing polysilicon film, and a second metal film in order from the side nearest to the semiconductor substrate, the second wiring includes the first metal film, the impurity-containing polysilicon film, and the second metal film in order from the side nearest to the semiconductor substrate, and the first and second gate insulating films include a high-dielectric insulating film higher in dielectric constant than oxide silicon.
 8. The semiconductor device according to claim 7, wherein the third wiring includes the impurity-containing polysilicon film and the second metal film.
 9. The semiconductor device according to claim 2, wherein the first transistor is an N-channel transistor, and the second transistor is a P-channel transistor.
 10. A method for manufacturing a semiconductor device, comprising: preparing a semiconductor substrate including a first well, a second well, and an isolation region between the first well and the second well with respect to a first direction; forming a first conductive film which is located on the first well and one end of which in the first direction is positioned on the isolation region, and a second conductive film which is located on the second well and one end of which in the first direction is positioned on the isolation region; forming a third conductive film, so as to extend from a space on the first conductive film through a space on the isolation region to a space on the second conductive film with respect to the first direction, and have a concave shape on the isolation region; forming a buried insulating film on the third conductive film, so as to fill a concave portion of the third conductive film on the isolation region; patterning the first to third conductive films and the buried insulating film to form a first wiring on the first well, a second wiring on the second well, and a concave third wiring and a buried insulating film on the isolation region; forming an interlayer insulating film on the semiconductor substrate; removing a portion of the interlayer insulating film until the buried insulating film is exposed; forming a contact plug, so as to penetrate through the interlayer insulating film, resulting in contacting with at least one of the first and second wells; and forming a plurality of fourth wirings, so as to contact with the buried insulating film on the third wiring.
 11. The method for manufacturing a semiconductor device according to claim 10, wherein the buried insulating film is formed by an ALD method or a low-pressure CVD method in forming the buried insulating film.
 12. The method for manufacturing a semiconductor device according to claim 10, further comprising forming a first insulating film by a plasma CVD method between forming the third conductive film and forming the buried insulating film.
 13. The method for manufacturing a semiconductor device according to claim 10, further comprising forming a second insulating film on the buried insulating film by a plasma CVD method, following forming the buried insulating film.
 14. The method for manufacturing a semiconductor device according to claim 13, wherein the second insulating film is removed in removing the portion of the interlayer insulating film.
 15. The method for manufacturing a semiconductor device according to claim 10, further comprising, between forming the first to third wirings and the buried insulating film and forming the interlayer insulating film: forming a first source and drain on both sides of the first wiring within the first well; and forming a second source and drain on both sides of the second wiring within the second well, wherein a first transistor including the first source and drain and the first wiring as a first gate electrode is formed, and a second transistor including the second source and drain and the second wiring as a second gate electrode is formed.
 16. The method for manufacturing a semiconductor device according to claim 15, wherein the first transistor is an N-channel transistor, and the second transistor is a P-channel transistor.
 17. The method for manufacturing a semiconductor device according to claim 10, wherein the first well, the second well and the isolation region are located in a peripheral circuit region of the semiconductor substrate, the method further comprises: forming a third transistor including a third source and drain in a memory cell region of the semiconductor substrate, between preparing the semiconductor substrate and forming the first to third wirings and the buried insulating film; and forming a capacitor electrically connected to one of the third source and drain, following forming the fourth wirings.
 18. The method for manufacturing a semiconductor device according to claim 10, wherein the first conductive film includes a first metal film and an impurity-containing polysilicon film in order from the side nearest to the semiconductor substrate, and the second conductive film includes the first metal film and the impurity-containing polysilicon film in order from the side nearest to the semiconductor substrate.
 19. The method for manufacturing a semiconductor device according to claim 18, wherein the third conductive film includes the impurity-containing polysilicon film and a second metal film in order from the side nearest to the semiconductor substrate. 